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NAME

       MPI_Barrier -  Blocks until all process have reached this routine.

SYNOPSIS

       #include "mpi.h"
       int MPI_Barrier (
               MPI_Comm comm )

INPUT PARAMETERS

       comm   - communicator (handle)

NOTES

       Blocks  the caller until all group members have called it; the call returns at any process
       only after all group members have entered the call.

ALGORITHM

       If the underlying device cannot do better, a tree-like or combine  algorithm  is  used  to
       broadcast  a  message  wto  all  members  of the communicator.  We can modifiy this to use
       "blocks" at a later time (see MPI_Bcast ).

NOTES FOR FORTRAN

       All MPI routines in Fortran (except for MPI_WTIME  and  MPI_WTICK  )  have  an  additional
       argument  ierr  at  the  end  of  the  argument list.  ierr is an integer and has the same
       meaning as the  return  value  of  the  routine  in  C.   In  Fortran,  MPI  routines  are
       subroutines, and are invoked with the call statement.

       All MPI objects (e.g., MPI_Datatype , MPI_Comm ) are of type INTEGER in Fortran.

ERRORS

       All  MPI  routines  (except MPI_Wtime and MPI_Wtick ) return an error value; C routines as
       the value of the function and Fortran routines in the last argument.  Before the value  is
       returned,  the current MPI error handler is called.  By default, this error handler aborts
       the MPI job.  The error handler may be changed with MPI_Errhandler_set  ;  the  predefined
       error  handler  MPI_ERRORS_RETURN  may be used to cause error values to be returned.  Note
       that MPI does not guarentee that an MPI program can continue past an error.

       MPI_SUCCESS
              - No error; MPI routine completed successfully.
       MPI_ERR_COMM
              - Invalid communicator.  A common error is to use a null  communicator  in  a  call
              (not even allowed in MPI_Comm_rank ).

LOCATION

       barrier.c

                                            11/14/2001                             MPI_Barrier(3)